Composite refractory body



Patented Sept. 22, 1925.

I UNITED STATES PAT OFFICE.

JOHN WESLEY MABDEN, OF EAST ORANGE, AND HENRY KNEELAND RICHARDSON, OF INEWARK, NEW JERSEY, ASSIGNORS '1 PORATION or PENNSYLVANIA. 1

O WESTINGHOUSE LAMP COMPANY, A. GOR- comrosrrn nnrnncronx BODY.

30 Drawing.

To all tvhom'z't may concern: Be it known that we, JOHN WESLEY. MAR-DEN, a citizen of the United States, and a resident of East Orange, inthe county of.

combination of refractory ceramic materials,

one of which is thorium oxide.

An object of this invention isthe provision of a method for economicallyand expeditiously producing refractory brick and other articles to atleast part of the of which thorium oxide is afiixed.

A special object of ouruinve'ntion is the production 'of composite brickparticularly useful for lining furnaces subject to high 26 temperatures.

- Other objects will be apparent from a reading of the followingdescription.

11 esses, it is desirable to prevent the contamiso nation of thematerial undergoing treatment.

This is miealsnytrue when investigations are'being'ihade of the metalswhich require high temperature treatment. It is known that suchrefractories as magnesia, lime and even zirconia cannot be used incontact with metals having such high melting points as tungsten ormolybdenum on account of the interaction between these metals and there-' fractor'y' oxides mentioned. In the case of a lime crucible, forexample, tungsten interacts with this oxide to yield volatile prodnotewhich are probably calcium metal and tungstic oxide. For this reason andmany others, attem ts have. been made to produce ii bricks and ot erarticles, used in connection with metallur 'cal investi ations, from therefractory oxi es, especial? thorium oxide.

Inasmuch as thorium oxi e,-"when-'highly heated, is one of the mostrefractor of substances and also because its chemica resistivity is verygreat it will be appreciated that an article, such as a brick or acrucible sursurface practicing many metallurgical proc- Applicationfiled June 23, 1922. Serial No; 570,479.

the sole material for constituting a manufactured refractory article, itis found desirable for several reasons to produce a com-. posite bodyhaving thoria as one of its constituents; for example, crucibles may belined with thorium oxide and thereby serve the same purpose equally wellif not better than a cruclble consisting practically of thoria only.Such a compositecrucible may be more desirable than a crucible of thorianot only from the standpoint of function but from that of econom It hasbeen found that by properly preparing a suitable paste or slip ofthorium oxide, the same may be firmly aflixed by certain processes, asfor example, by casting, to other ceramic refractory materials to formcomposite bodies such as crucibles, bricks,

tubes and the like.

In practicing our invention, the first step consists in forming asuspension of thorium oxide of a suitable consistency for casting. Thissuspension, which is usually termed the slip in theceramic industry, maybe pre- Bared by thoroughly grinding and mixing,

5 small. quantity of another refractory material to'serve as a filler, abinder salt, such, for example, as a double-fluoride salt which isadapted to serve as or functions similarly to a colloid and a smallquantity of a suitable acid which will cause any colloid prescut tocoagulate. When the mixture has been'ground very fine it is mixed withabout an equal art of thorium oxide which has been previously pulverizeduntil it is very fine. This mixture or slip is then dlluted with waterto give a suitable conslstency for castin after which it may be cast onto the sur ace of abody of ceramic materlal such as fire clay. The comosite body thus vformed is then dried carefu l vent cracking, afterwhich it is subjected to a firing process.

Another important conslderatlon is the drying of the casting, for, ifthe dry-mg ste is carried on too rapidly, the casting w 1 so as to pre-.

means of a ball mill, thorium oxide, a

crack. Generally speaking, the drying depends on the size of thearticle; the larger. the article, the longer the time required fordrying. Furthermore, the drying temperature should be gradually raiseduntil the maximum temperature for dehydration has been reached, at whichtemperature the drying operation should be continued for a shortinterval.

In making a composite brick. consisting in part of thoria, first preparea mixture consisting of approximately nine parts of thoria which hasbeen previously ignited at about l300 (1', about one part of zirconia,about one part of a double salt of a halide, such, for example, aspotassium-thorium fluoride, potassium-zirconium fluoride, cryolite, orthe likefand a one-half part of phosphoric or other Suitable acid. Themlxture is ball milled wet and, after it has been ground very fine inthis way, it is mixed with an equal part of ignited thoria which hasbeen pulverized in the mortar to pass a 200 mesh sieve.

This mixture is diluted with water to give a suspension or slip ofsuitable consistency for casting. b

This slip may then be poured over at least a portion of the surface of afire clay brick to form a coating of any desired thickness. Thecomposite body thus formed is then allowed to dry. in drying, it isimportant to avoid cracking the material and therefore the preferableprocedure in performing this step is as follows. The composite brickshould be placed in a drying oven and brought gradually from roomtemperature to about 60 C. within a period of about at hours. The part1dried brick is then heated to about 120 to expel the remaining moisture.This heat treatment is continued for about two hours, or untilpractically all moisture has been expelled.

The brick is next fired by being placedin any suitable furnace. Thetemperature of the furnace is gradually increased until a temperatureequal to the sintering temperature of the fire cla hasbeen attained,which may va from a out11400 C. to 1800 0. During t 'e firing process,most of the salts volatilize, the final composition of the brick .beingpractically a; base of fire clay covered with thoria containing a slightamount of zircoma. The brick, upon removal from .the furnace, should bepermitted to cool slowly.

While one method forproducing a composlte refractory material has beendescribed in detail, it is to be understood that minor modifications maybe madec without afiecting the scope of the invention which is limitedonly by the appended claims.

What is claimed is: 1. As an article of manufacture a composite bodycomprising a ceramic refractory Lea-asst posite brick comprising aceramic refractory material to the surface of which, at least in part, acoating of substantial thickness of practically pure thorium oxide isafiixed.

4. As an article of manufacture a composite brick comprising fire clayas a base to the surface of which, at least in part, pure thorium oxideis afixed.

,5. As an article of manufacture a ceramic body having asurface areathereof covered with a mixture of pure thorium oxide and a small portionof. substantially pure zirconium oxide.

6. As an article of manufacture a composite body of refractory ceramicmaterial having as a surface portion of substantial thickness, a mixtureof pure thorium and zirconium oxides.

7. As an article of manufacture a composite refractory body comprising aportion of ceramic material and a highly refractory compositioncontaining pure thorium oxide and a small portion of substantially purezirconium oxide affixed thereto.

8. The method of roducing a composite refractory body. which comprisespreparing a slip of finely divided thorium oxide, a salt adapted tofunction similarly to a colloid, a medium. adapted to precipitate anycolloid and to produce a suitable consistency for basting, subsequentlyapplying the thus formed slip to ceramic material and drying.

9. The method of producing a composite refractory body which comprisespreparing a paste comprising finely divided thorium oxlde, a filler, adouble salt adapted to serve as a colloid, a coagulating medium and asufficientquantity of fluid to produce a suitable conslstency forcasting, subsequently applyin said paste to a ceramic material, dryingfihe composite body and later firing the same.

10. .The method of producing a composite refractory body which comprisespreparing a paste comp-using finely divided thorium oxide, a filler suchas zirconia, a double salt adapted to serve as a colloid, such aspotassium-thorium fluoride, potassium-zirconium fluoride, cryo-lite andthe like, a coagulating medium such as phosphoric acid and the like anda Sufiicientquantity of fluid to produce a suitable consistency forcasting, subsequently coating said paste upon a mass of ceramic materialsuch as fire clay, drying the composite bod and later firing the same.

11. The metho of producing acomposite refractory article which consistsin forming a paste by ball milling in the wet state llllti a mixture ofabout nine parts thoria, about ing the composite body thus formed aiidsubon'e paifrt zirconia, about one part potasseque-ntly firing the same.10 shim-thorium fluoride and about one-half In testimony whereof, wehave hereunto part phosphoric acid then mixing with said subscribed ournames this 22nd day of June, paste an equal part of ignited thoria,subse- 1922. i i

quently forming a slip of suitable consistency for casting by addingwater, casting JOHN WESLEY MARDEN.

said slip on a body of ceramlc material, dry- HENRY KN EELAN DRICHARDSON.

